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Boulton Paul P.31 Bittern

The Boulton Paul Bittern was a 1920s British night-fighter aircraft, it was named after the marsh bird.

Designed to Air Ministry Specification 27/24, which called for a single-seat night fighter for use against enemy bomber aircraft, the Bittern design was unusual for its time in that it was a twin-engined shoulder wing monoplane rather than a single-engine biplane.

Two prototypes were built.

The first was a cantilever wing design with the engines, 214 hp Armstrong Siddeley Lynx, on the leading edge of the wing.

However initial trials showed that the wing was too flexible and so wing struts were added fixed between the bottom of the fuselage and the engine installations.

However this added weight and drag with a commensurate effect on performance.

The second prototype had the engines suspended from the wings on the struts.

During testing performance was so poor that further development was abandoned.



32 ft 4 in (9.86 m)


41 ft 0 in (12.50 m)

Empty weight

3,215 lb (1,458 kg)

Gross weight

4,500 lb (2,041 kg)


2 × Armstrong Siddeley Lynx 7-cyl.

Air-cooled radial piston engine, 230 hp (170 kW) each


Maximum speed

1st Protoype, 145 mph (233 km/h, 126 kn) 2nd Prototype, 152 mph (245 km/h)


3+3⁄4 hours



2 x fixed forward firing 0.303 in (7.70 mm) Vickers machine-guns.

2 x two 0.303 in (7.70 mm) Lewis machine guns in revolving barbettes either side of the nose.

Night landing flares under the fuselage.

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